docs: def generate_exact(self, model, vcpu_num, host_cpu):
          """
          Generate exact CPU model with nested virtualization CPU feature.
  
          Args:
              model(str): libvirt supported CPU model
              vcpu_num(int): number of virtual cpus
              host_cpu(lxml.etree.Element): the host CPU model
  
          Returns:
              lxml.etree.Element: CPU XML node
          """
  
          nested = {'Intel': 'vmx', 'AMD': 'svm'}
          cpu = ET.Element('cpu', match='exact')
          ET.SubElement(cpu, 'model').text = model
          cpu.append(self.generate_topology(vcpu_num))
  
          vendor = host_cpu.findtext('vendor')
          if not nested.get(vendor):
              LOGGER.debug(
                  'Unknown vendor: {0}, did not configure nested '
                  'virtualization cpu flag on guest.'.format(vendor)
              )
              return cpu
  
          model_vendor = LibvirtCPU.get_cpu_vendor(family=model)
          if vendor != model_vendor:
              LOGGER.debug(
                  (
                      'Not enabling nested virtualization feature, host '
                      'vendor is: {0}, guest vendor: '
                      '{1}'.format(vendor, model_vendor)
                  )
              )
              return cpu
  
          flag = nested[vendor]
          if host_cpu.find('feature/[@name="{0}"]'.format(flag)) is not None:
              cpu.append(self.generate_feature(name=flag))
          else:
              LOGGER.debug(
                  (
                      'missing {0} cpu flag on host, nested '
                      'virtualization will probably not '
                      'work.'
                  ).format(flag)
              )
  
          return cpu